Siloxane epoxy polymers as metal diffusion barriers to reduce electromigration

ABSTRACT

Structures employing siloxane epoxy polymers as diffusion barriers adjacent conductive metal layers are disclosed. The siloxane epoxy polymers exhibit excellent adhesion to conductive metals, such as copper, and provide an increase in the electromigration lifetime of metal lines. In addition, the siloxane epoxy polymers have dielectric constants less then 3, and thus, provide improved performance over conventional diffusion barriers.

FIELD OF THE INVENTION

The present invention relates to semiconductor devices in whichmetallization/dielectric diffusion barrier materials are employed, andmore particularly to the use of siloxane epoxy polymers as diffusionbarrier caps in such devices.

BACKGROUND OF THE INVENTION

Conventional semiconductor devices typically comprise a semiconductorsubstrate, normally of doped monocrystalline silicon, and a plurality ofsequentially formed dielectric layers and conductive patterns. Anintegrated circuit is formed containing a plurality of conductivepatterns comprising conductive lines separated by inter-wiring spacings.Typically, the conductive patterns on different layers, i.e., upper andlower layers, are electrically connected by a conductive plug filling avia hole, while a conductive plug filling a contact hole establisheselectrical contact with an active region on a semiconductor substrate,such as a source/drain region or a gate/metal region. Conductive linesare formed in trenches, which typically extend substantially horizontalwith respect to the semiconductor substrate. Semiconductor chipscomprising eight or more levels of metallization are becoming moreprevalent as device geometries have shrunk to half-micron levels and toa tenth of a micron levels.

A conductive plug filling a via hole is typically formed by depositingan interlayer dielectric on a conductive layer comprising at least oneconductive pattern. Generally, a dielectric barrier or capping layer(also referred to herein as a “diffusion barrier”) is deposited onto theconductive layer prior to deposition of the dielectric. Next, an openingin the dielectric layer is formed by conventional photolithographic andetching techniques, and the opening is filled with a conductive metal,such as tungsten, aluminum, copper, or a copper alloy. Excess conductivematerial on the surface of the dielectric layer is typically removed bychemical mechanical polishing (CMP). After depositing a diffusionbarrier on the metal and exposed surface of the dielectric layer, asecond interlayer dielectric is typically deposited onto the barrier.

One such fabrication method is known as damascene and basically involvesforming an opening in the interlayer dielectric and filling the openingwith a conductive metal. Dual damascene techniques involve forming anopening comprising a lower contact or via hole section in communicationwith an upper trench section, which opening is filled with a conductivemetal, to simultaneously form a conductive plug and electrical contactwith a conductive line.

FIG. 1 is a cross-sectional view of a portion 10 of a prior art,conventional semiconductor metal interconnect structure fabricated usingdamascene processing, wherein trenches (lines) (not shown) and a via(hole) 20 are etched into interlayer dielectric 30, which is disposedatop a semiconductor substrate 15. Conductive metal 50 is deposited intovia 20 and planarized. In this embodiment, Ta-based liner 40, made oftantalum, TaN, or TaSiN, is conformally deposited onto sidewalls 21 aand 21 b and bottom 22 of via 20 (and any trenches, not shown), prior todeposition of metal 50 and planarization. Dielectric barrier 60,traditionally made of SiN, SiC, SiCH, or SiCN, atop metal 50 acts as adiffusion barrier, as well as an etch stop layer. A second dielectric ormetal 70 is then deposited atop dielectric barrier 60.

Disadvantageously, however, the atomic transport at the metal/diffusionbarrier interface 61 is the most important contributor toelectromigration of the metal. Since conductive metals, such as Cu, donot adhere well to the traditional dielectric barrier materials, theinterface provides the fastest interfacial diffusion path. Priorsolutions to reducing electromigration include using a metallic-basedcap (Ta, Pd, or CoWP) for the metal lines, but the increase in thefabrication complexity and in the effective resistivity are undesirable.

Thus, it is known that a diffusion barrier or capping material is neededbetween the metal and dielectric to reduce the amount of metal diffusioninto the neighboring dielectric material. However, because interfacialdiffusion at the metal/diffusion barrier interface is the majorcontributor to reduction in the life-time associated with theelectromigration failure in integrated circuits (IC), it is desirable toimprove the interfacial bonding at such interfaces to reduce andeliminate the interfacial diffusion. The use of traditional diffusionbarriers such as SiN, SiC, SiCH, and SiCN only provide marginal success.

Furthermore, the aforementioned traditional diffusion barriers havedielectric constants larger than 6. It is known, however, that loweringthe overall dielectric constants (κ values) of the dielectric layersemployed in metal interconnects lowers the resistance capacitance (RC)product of the chip and improves its performance. The high κ values oftraditional diffusion barriers increase the overall κ value of thestructure and are therefore not acceptable for future high speed ICs.

Thus, a need exists in the semiconductor industry for a diffusionbarrier material having improved adhesion to the conductive metal,thereby reducing interfacial metal diffusion. It would also beparticularly advantageous if such a material could have a dielectricconstant of 3.9 or lower, thereby reducing the overall κ value of thefinal structure.

SUMMARY OF THE INVENTION

The present invention meets the aforementioned needs and providessemiconductor structures which include a diffusion barrier materialhaving unexpectedly improved adhesion to conductive metals. Inparticular, the present invention reduces electromigration insemiconductor devices through the utilization of siloxane epoxy polymersas diffusion barriers or capping materials. Furthermore, the siloxaneepoxy polymers discussed herein have dielectric constants less then 3,and can therefore provide much better performance than the conventionaldiffusion barriers. Advantageously, the same low κ dielectric materialcould then also be used as the interlayer dielectric betweenmetallization layers.

Therefore, the present invention relates to a structure comprising aconductive layer and a diffusion barrier disposed onto a surface of theconductive layer. The conductive layer comprises a conductive metal, andthe diffusion barrier comprises a first layer and a second layer. Thefirst layer is adjacent to both the second layer and to the surface ofthe conductive layer. Furthermore, the first layer and the second layerare each independently selected from the group of siloxane epoxypolymers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section of a prior art metal interconnect portion of asemiconductor structure utilizing a traditional diffusion barrier;

FIG. 2 is a cross-section of a structure illustrating an embodiment ofthe diffusion barrier of the present invention disposed onto a surfaceof a conductive layer;

FIG. 3 is a cross-section of the structure of FIG. 2 showing an optionaldielectric material disposed on the diffusion barrier of the presentinvention;

FIG. 4 is a graph of capacitance vs. voltage (C vs. V) representing theTriangular Voltage Sweep (TVS) data for as-deposited and for annealed(250° C.) Si/polymer dielectric/adhesion promoter/Cu samples, whichshows that no Cu diffusion into the polymeric dielectric was observed ineither case; and

FIG. 5 is a graph of current density vs. time (I vs. t) for annealed(250° C.) Si/polymer dielectric/adhesion promoter/Cu samples, whichindicates that the leakage current property does not degrade with time.

DETAILED DESCRIPTION OF THE INVENTION

The present invention employs siloxane epoxy polymers in place ofconventional dielectrics or metal-based caps currently being employed asdiffusion barriers for metal interconnects in semiconductor structures.The polymers described herein exhibit excellent adhesion to metals, suchas copper, and provide an increase in the electromigration lifetime ofmetal lines.

FIGS. 2-3 each depict a structure 100 in which the diffusion barriersystem of the present invention has been incorporated. In each of FIGS.2-3, conductive layer 500 has been provided with an adjacent metaldiffusion barrier 600 disposed thereon. FIG. 3 includes optionaldielectric layer 700 disposed onto diffusion barrier 600. Typically, thestructures of FIGS. 2 and 3 would be disposed onto a dielectric material(not shown) disposed onto a semiconductor substrate (not shown) and usedin semiconductor devices, which employ conventional damasceneprocessing, as previously described, one of which is depicted in FIG. 1.In addition, it should be noted that the invention also includessemiconductor structures in which the materials depicted in FIGS. 2-3are deposited over a substrate (not shown) in reverse order.

As used herein, the term “semiconductor substrate” refers to substratesknown to be useful in semiconductor devices, i.e. intended for use inthe manufacture of semiconductor components, including, but not limitedto, focal plane arrays, opto-electronic devices, photovoltaic cells,optical devices, transistor-like devices, 3-D devices,silicon-on-insulator devices, super lattice devices and the like.Semiconductor substrates include integrated circuits preferably in thewafer stage having one or more layers of wiring, as well as integratedcircuits before the application of any metal wiring. Furthermore, asemiconductor substrate can be as simple as the basic wafer used toprepare semiconductor devices. The most common such substrates used atthis time are silicon and gallium arsenide.

FIG. 2 is a cross-sectional view of structure 100 illustrating anembodiment of the present invention. In FIG. 2, conductive layer 500made of a conductive metal has been formed. The conductive metal istypically aluminum, an aluminum alloy, tungsten, cobalt, a metalsilicide, copper, or a copper alloy. However, the conductive metal ispreferably copper or a copper alloy because copper has a lowerresistivity than aluminum and improved electrical properties compared totungsten. Thus, copper is a very desirable metal for use as a conductiveplug as well as conductive wiring.

Diffusion barrier 600 is disposed onto surface 510 of conductive layer500. One primary purpose of barrier 600 is to serve as a diffusionbarrier to prevent diffusion of copper or other conductive metal fromconductive layer 500 into the surrounding dielectric material (shown inFIG. 3). Diffusion barrier 600 also protects conductive layer 500 duringsubsequent etching of an overlying dielectric layer.

Diffusion barrier 600 comprises two adjacent layers 610 and 620, whereineach layer independently comprises a siloxane epoxy polymer, asdescribed herein. First layer 610 acts as an adhesion promoter, andsecond layer 620 prevents metal diffusion. Adhesion promoter layer 610is adjacent surface 510 of conductive metal layer 500.

Formation of diffusion barrier 600 is done by first depositing adhesionpromoter layer 610 comprising a siloxane epoxy polymer described hereinonto surface 510 of conductive layer 500 to a thickness ranging fromabout 0.001 μm to about 3 μm, but preferably ranging from about 0.01 μmto about 0.03 μm, by any known method, such as spin casting (alsoreferred to herein as “spin coating”), dip coating, roller coating, ordoctor blading, for example. Typically, spin casting is used.

After deposition, the siloxane epoxy polymer adhesion promoter layer 610and adjacent metal layer 500 are typically dried to remove solvent fromthe polymer solution, followed by curing and annealing, as describedherein. Good adhesion of the polymer to the metal is assured because ofthe polymer/metal interaction at interface 510.

Next, adjacent siloxane epoxy polymer barrier layer 620 is depositedonto dried/cured adhesion promoter layer 610 to a thickness ranging fromabout 0.02 μm to about 10 μm, but preferably ranging from about 0.02 μmto about 0.05 μm by any of the aforementioned methods. Again,spin-casting is typically employed. Drying and curing steps, followed byannealing, as described herein, are then performed to cross-link polymer620.

However, prior to deposition of siloxane epoxy polymer barrier layer 620onto adhesion promoter layer 610, surface 615 of adhesion promoter layer610 typically undergoes a surface treatment to promote wetting andadhesion of subsequently deposited polymer 620. An exemplary surfacetreatment is described in the aforementioned related U.S. patentapplication being filed concurrently herewith under Ser. No. 10/832,629and entitled “CHEMICAL TREATMENT OF MATERIAL SURFACES”. Briefly, thetreatment involves contacting the cured polymer surface 615 with anaqueous solution of sulfuric acid or phosphoric acid and rinsing it offwith water, followed by drying.

The siloxane epoxy polymers described herein are unlike many otherpolymers, which do not adhere well to metals and which allow diffusionof metallic ions/atoms at high process/use temperatures and electricfields, invariably both imposed at the same time. Furthermore, thesiloxane epoxy polymers used in the present structures allow excellentadhesion to metals, while at the same time metal diffusion into thepolymer matrix is inhibited. Thus, the siloxane epoxy polymers are verysuitable for use in diffusion barriers and adhesion promoterapplications.

Exemplary preferred siloxane epoxy polymers suitable for use as adhesionpromoter layer 610 and/or diffusion layer 620 include those commerciallyavailable from Polyset Company as PC 2000, PC 2003, PC 2000HV, each ofwhich has the following structure (I).

wherein m is an integer from 5 to 50. The molecular weights of thesepolymers range from about 1000 to about 10,000 g/mole.

Other suitable siloxane epoxy polymers for use as layer 610 and/or 620of diffusion barrier 600 include random and block copolymers having thefollowing general following formula (II):

wherein the X monomer units and Y monomer units may be randomlydistributed in the polymer chain. Alternatively, like repeating units, Xand Y, respectively, may occur together in a block structure. Thepolymers of structure (II) are advantageous because they haveunexpectedly low dielectric constants of less than 3. Therefore, theyare useful as diffusion barriers, as well as low k interlayer dielectricmaterials, as described in the aforementioned related U.S. applicationentitled “SILOXANE EPOXY POLYMERS FOR LOW-κ DIELECTRIC APPLICATIONS”being filed concurrently herewith under Ser. No. 10/832,515.

Preferably, in formula (II), R¹ and R² are each independently methyl,methoxy, ethyl, ethoxy, propyl, butyl, pentyl, octyl, and phenyl, and R³is methyl or ethyl. In addition, p is an integer ranging from 2 to 50;and q is 0 or an integer ranging from 1 to 50. Most preferably, R³ inthe terminal residues at the end of the polymer chain is methyl,resulting in a polymer having structure (IIA).

Exemplary polymers having structure (IIA) include, but are not limitedto, Polyset's PC 2010, PC 2021, and PC 2026. In PC 2010, R¹ and R² instructure (IIA) are both phenyl groups, and the ratio of p to q rangesfrom about 8:1 to about 1:1, but is usually about 4:1 to about 2:1. Themolecular weight of PC 2010 ranges from about 5000 to about 7500 g/mole.In PC 2021, R¹ and R² are both methyl groups, as shown in structure(IIB), and the ratio of p to q ranges from about 8:1 to about 1:1, butis usually about 4:1 to about 2:1. The molecular weight of PC 2021ranges from about 2000 to about 7500 g/mole. In PC 2026, R¹ istrifluoropropyl, and R² is a methyl group. The ratio of p:q is typicallyabout 3:1. The molecular weight of PC 2026 ranges from about 5000 toabout 7500 g/mole.

Siloxane epoxy polymers of structure (II) containing monomer units X andY may be synthesized by base-catalyzed hydrolysis and subsequentcondensation of alkoxy silane monomers, using 0.5 to 2.5 equivalents ofwater in the presence of an ion exchange resin, such as Amberlyst A-26,Amberlite IRA-400 and Amberlite IRA-904 from Rohm & Haas, in thepresence of an alcohol solvent, followed by separation of the siloxaneoligomer from the water/solvent mixture. The procedure for thepolymerization is described fully in U.S. Pat. Nos. 6,069,259 and6,391,999 and copending, commonly assigned U.S. application Ser. No.10/269,246 filed Oct. 11, 2002.

In structure (II), the alkoxy silane monomer from which the X units arederived may be 2-(3,4-epoxycyclohexylethyl)trimethoxy silane, which iscommercially available as A-186 from Witco Corporation. Exemplarymonomers used to provide the Y units include tetraethoxysilane(ethylorthosilicate), tetramethoxysilane (methylorthosilicate),tetraisopropoxysilane, methyltrimethoxysilane, ethyltriethoxysilane,hexyltriethoxysilane, cyclohexyltrimethoxysilane,1,1,1-trifluoroethyltriethoxysilane, phenyltriethoxysilane,phenylmethyldiethoxysilane, phenylmethyldimethoxysilane,diphenyldimethoxysilane (used in PC 2010),2-phenylethyltrimethoxysilane, benzyltriethoxysilane,vinyltrimethoxysilane, dimethyldimethoxysilane (used in PC 2021),methylpropyldimethoxysilane, dipropyldimethoxysilane,dibutyldimethoxysilane, methylpentyldimethoxysilane,dipentyldimethoxysilane, dioctyldimethoxysilane, dimethyldiethoxysilane,trimethylmethoxysilane, diethyldimethoxysilane, allyltrimethoxysilane,divinyldimethoxysilane, methyvinyldimethoxysilane,bis(triethoxysilyl)methane, bis(triethoxysilyl)ethane,butenyltrimethoxysilane, trifluoropropylmethyldimethoxysilane (used inPC 2026), 3-bromopropyltrimethoxysilane,2-chloroethylmethyldimethoxysilane,1,1,2,2-tetramethoxy-1,3-dimethyldisiloxane, phenyltrimethoxysilane.Also, useful in these mixtures are trimethoxysilyl-terminatedpolydimethylsiloxanes as well as the corresponding hydroxyl-terminatedpolydimethylsiloxanes. The foregoing monomers are either commerciallyavailable or readily synthesized by reactions well known in the art.

One preferred material for use as layer 610 and/or 620 of diffusionbarrier 600 is the siloxane epoxy polymer having structure (IIB) above(PC 2021), which may be synthesized from2-(3,4-epoxycyclohexylethyl)trimethoxy silane (A-186) (to form the Xunits), and dimethyldimethoxysilane (to form the Y units).Dimethyldimethoxysilane is commercially available United ChemicalTechnology or readily synthesized by reactions well known in the art. Aspreviously mentioned, the ratio of p to q ranges from about 8:1 to about1:1, but is usually about 4:1 to about 2:1. The polymer of structure(IIB) has a surprisingly low dielectric constant ranging from about 2.2to about 2.7.

As previously mentioned, after deposition, each siloxane epoxy polymerlayer may be cured by art-recognized techniques, such as thermally or byusing actinic radiation, such as U.V. or electron beam. However, priorto curing, the polymers may be dried under vacuum to remove solvent fora time ranging from about 0.5 to about 2 hours, and a temperatureranging from about 80° C. to about 120° C., but typically about 1 hourat about 100° C.

Curing of the polymer is effected in the presence of a cationicpolymerization initiator such as a diazonium, sulfonium, phosphonium, oriodonium salt, but more preferably a diaryliodonium,dialkylphenacylsulfonium, triarylsulfonium, or ferrocenium salt photoinitiator.

A preferred polymerization cationic initiator is a diaryliodonium saltselected from the group having formulae (III), (IV), (V), (VI), and(VII)

wherein each R¹¹ is independently hydrogen, C₁ to C₂₀ alkyl, C₁ to C₂₀alkoxyl, C₁ to C₂₀ hydroxyalkoxyl, halogen, and nitro; R¹² is C₁ to C₃₀alkyl or C₁ to C₃₀ cycloalkyl; y and z are each independently integershaving a value of at least 5; [A]⁻ is a non-nucleophilic anion, commonly[BF₄]⁻, [PF₆]⁻, [AsF₆]⁻, [SbF₆]⁻, [B(C₆F₅)₄]⁻, or [Ga(C₆F₅)₄]⁻. Thesediaryliodonium salt curing agents are described in U.S. Pat. Nos.4,842,800; 5,015,675; 5,095,053; 5,073,643; and 6,632,960.

Preferably, the cationic polymerization initiator is dissolved in3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexane carboxylate,dicyclopentadiene dioxide, or bis(3,4-epoxycyclohexyl) adipate to form acatalyst solution which contains from about 20 to about 60 parts byweight of the selected cationic initiator and from about 40 to about 80parts by weight of 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexanecarboxylate, dicyclopentadiene dioxide, or bis(3,4-epoxycyclohexyl)adipate. When the cationic polymerization initiator is a diaryliodoniumsalt, the catalyst solution preferably contains about 40 parts by weightof the diaryliodonium salt curing agent and about 60 parts by weight3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexane carboxylate,dicyclopentadiene dioxide, or bis(3,4-epoxycyclohexyl) adipate.

Typically, from about 0.1 to about 5 parts by weight of the catalystsolution is added to an appropriate amount of siloxane epoxy polymerresin (ranging from about 95 to about 99.9 parts by weight siloxaneepoxy polymer).

Preferred diaryliodonium salts include[4-(2-hydroxy-1-tetradecyloxy)-phenyl]phenyliodoniumhexafluoroantimonate having formula (VI), wherein [A]⁻ is [SbF₆]⁻, andR¹² is C₁₂H₂₅ (available from Polyset Company, as PC-2506);[4-(2-hydroxy-1-tetradecyloxy)-phenyl]phenyliodoniumhexafluorophosphate, wherein in formula (VI), [A]⁻ is [PF₆]⁻, and R¹² isC₁₂H₂ (available from Polyset Company as PC-2508);[4-(2-hydroxy-1-tetradecyloxy)-phenyl]4-methylphenyliodoniumhexafluoroantimonate (formula (VII)), wherein [A]⁻ is [SbF₆]⁻, and R¹²is C₁₂H₂₅ (available from Polyset Company as PC-2509), and[4-(2-hydroxy-1-tetradecyloxy)-phenyl] 4-methylphenyliodoniumhexafluorophosphate (formula (VII)), wherein [A]⁻ is [PF₆]⁻, and R¹² isC₁₂H₂₅ (available from Polyset Company as PC-2519). The preparation ofcationic initiators having formula (VII) is discussed in theaforementioned U.S. Pat. No. 6,632,960.

Depending on the thickness of the film, thermal curing is generallyperformed by heating the deposited polymer solution to a temperatureranging from about 155° C. to about 360° C., but preferably about 165°C., for a period of time ranging from about 0.5 to about 2 hours. Informulations curable by U.V. light, the films may be flood exposed byU.V. light (>300 mJ/cm²@ 250-380 nm). Curing by E-beam radiation isoften done at a dosage ranging from about 3 to about 12 Mrad. E-beamcuring is described in U.S. Pat. Nos. 5,260,349 and 4,654,379. Theparticular polymer formulation will determine which curing method willbe used, as one of skill would know. Following curing, a thermal annealwill often be employed under nitrogen or other inert gas at temperaturesranging from about 200° C. to about 300° C., but preferably about 250°C. for a period of time ranging from about 1 to about 3 hours, butpreferably about 2 hours. However, it should be noted that when theconductive layer is deposited onto the adhesion promoter layer, a finalthermal anneal, and even drying and curing are generally not performedon the adhesion promoter layer in order to permit the polymer surface toremain activated for reaction with the metal. The reaction between theadhesion promoter layer and the conductive layer is thus promoted bydrying, curing, and annealing the entire structure.

Furthermore, by changing the formula of the polymer, by varying itsconcentration, and the thickness of the deposited film, the onset curingtemperature and the speed of cure can be adjusted within a widelatitude.

Typically, when the siloxane epoxy films are thermally cured, the amountof catalyst can be decreased dramatically relative to the amount ofphotocatalyst needed to effect a cure induced by actinic radiation. Forinstance, in a thermal treatment, an exemplary siloxane resincomposition contains about 0.1 wt. % catalyst (i.e. 0.1 parts by weightcatalyst solution and about 99.9 parts by weight siloxane polymer,wherein an exemplary catalyst solution is a 40 wt. % solution of[4-(2-hydroxy-1-tetradecyloxy)-phenyl]phenyliodoniumhexafluoroantimonate (Polyset PC-2506) dissolved in3,4-epoxycyclohexylmethyl 3′,4′-epoxycyclohexanecarboxylate (UnionCarbide ERL-4221E)). By contrast, when the curing process is done byphoto-irradiation, the amount of the catalyst is generally about 4 wt. %(i.e. 4 parts by weight catalyst solution and 96 parts polymer).

FIG. 3 shows an embodiment wherein optional dielectric material 700 hasbeen disposed, typically as an interlayer dielectric betweenmetallization layers, onto exposed surface 630 of diffusion barrier 600to a thickness ranging from about 0.02 μm to about 2 μm, but preferablyranging from about 0.1 μm to about 0.7 μm. However, prior to depositionof dielectric material 700 onto diffusion barrier 600, exposed surface630 typically undergoes a surface treatment to promote wetting andadhesion of subsequently deposited dielectric 700, as previouslydescribed. Exemplary dielectric materials include, but are not limitedto, polyimides, parylene (poly-p-xylylene), polynaphthalene,benzocyclobutane (BCB), silicon-containing organic polymers, such asmethyl silsesquioxane (MSQ), and hydrogen silsesquioxane (HSQ), andaromatic hydrocarbon polymers, such as SiLK™, which contains phenyleneand carbonyl groups in the main chain, Nautilus™, and FLARE™, which is apoly(arylene) ether. SiLK™ and Nautilus™ are available from Dow ChemicalCompany. FLARE™ is manufactured by Allied Signal. Other dielectricmaterials include the siloxane epoxy polymers described herein. Aspreviously noted, siloxane epoxy polymer having formula (IIB) has adielectric constant ranging from about 2.2-2.7, and is therefore apreferred low k dielectric material for use as an interlayer dielectricbetween metallization layers.

Furthermore, it should be noted that a typical integrated circuitstructure may have eight or more interconnect (metal) layers stacked ontop of each other. Interposed between each metal layer is a dielectriclayer. Accordingly, the present invention also embraces these multilevelstructures wherein a metal diffusion barrier comprising adjacentsiloxane epoxy polymer layers separates a metal interconnect layer froma corresponding dielectric layer.

The following examples are given by way of illustration and are notintended to be limitative of the present invention. The reagents andother materials used in the examples are readily available materials,which can be conveniently prepared in accordance with conventionalpreparatory procedures or obtained from commercial sources.

EXAMPLE 1

N-type, 4-inch silicon wafers having a resistivity of 0-0.02 ohm-cm forMIM (metal-insulator-metal) structures were used as the substrates.After standard RCA cleaning an adhesion layer (HMDS) was spin-coatedonto each wafer at 3000 rpm for 40 sec. The wafers were then annealed inair at 100° C. for 10 min. A siloxane epoxy polymer solution containingformula (IIB), wherein the ratio of p to q was about 2:1, wasspin-coated onto each wafer at 3000 rpm for 100 sec to a thickness of0.5 μm. Onto the deposited polymer films, copper metal thin films weredeposited to a thickness of 0.3 μm using sputtering or e-beamevaporation. The Cu/polymeric film/wafers were then dried under vacuumof 10⁻³ torr for 1 hour at 100° C. The samples were then cured at 165°C. for 2 hours to cross-link the polymer, followed by a thermal annealat 250° C. under nitrogen gas flow for 1 hour. These films passed theindustry-accepted Scotch® tape adhesion test, which was executed usingcommercially available Scotch® tape attached to the film surface,followed by pulling the tape at a 90° angle to the sample.

EXAMPLE 2

The procedure of Example 1 was followed. Then a thin layer of anadhesion promoter was deposited onto the copper surface of each sample.The adhesion promoter was also a siloxane epoxy polymer solution havingformula (IIB), wherein the ratio of p to q was about 2:1, and wasspin-coated onto the copper films at 3000 rpm for 100 sec to a thicknessranging from about 0.01 μm to about 0.03 μm. The samples were then driedunder vacuum of 10⁻³ torr for 1 hour at 100° C., followed by curing at165° C. for 2 hours and a thermal annea at 250° C. under nitrogen gasflow for 1 hour to cross-link the polymer. The surface of the polymericadhesion promoter layer was then contacted with an aqueous solution ofsulfuric acid (50% by weight) for 30 seconds at room temperature,followed by removal of the acid solution by rinsing with deionized waterfor 30 seconds at room temperature and drying. A second layer comprisinga siloxane epoxy polymer solution containing formula (IIB), wherein theratio of p to q was about 2:1, was spin-coated onto the fully annealedand acid-treated adhesion promoter at 3000 rpm for 100 sec to athickness ranging from about 0.02 μm to about 0.05 μm. The whole stacks(wafer/polymeric film/Cu/adhesion promoter/diffusion barrier) were driedunder vacuum of 10⁻³ torr for 1 hour at 100° C., followed by curing at165° C. for 2 hours and a thermal anneal at 250° C. under nitrogen gasflow for 1 hour to cross-link the polymer. These samples also passed theaforementioned Scotch® tape tests.

EXAMPLE 3

N-type, 4-inch silicon wafers having a resistivity of 0-0.02 ohm-cm forMIM (metal-insulator-metal) structures were used as the substrates.After standard RCA cleaning, an adhesion layer (HMDS) was spin-coatedonto each wafer at 3000 rpm for 40 sec. The wafers were then annealed inair at 100° C. for 10 min. A siloxane epoxy polymer solution, acting asa diffusion barrier and containing formula (IIB), wherein the ratio of pto q was about 2:1, was spin-coated onto each wafer at 3000 rpm for 100sec to a thickness ranging from about 0.02 μm to about 0.05 μm. Thepolymeric film/wafers were dried under vacuum of 10⁻³ torr for 1 hour at100° C. The polymer films were then cured at 165° C. for 2 hours tocross-link the polymer, followed by a thermal anneal at 250° C. undernitrogen gas flow for 1 hour. The surface of the polymeric diffusionbarrier was then contacted with an aqueous solution of sulfuric acid(50% by weight) for 30 seconds at room temperature, followed by removalof the acid solution by rinsing with deionized water for 30 seconds atroom temperature and drying. A thin layer of an adhesion promotercomprising the siloxane epoxy polymer having formula (IIB), wherein theratio of p to q is about 2:1, was spin-coated onto the treated polymericfilms at 3000 rpm for 100 sec. to a thickness ranging from about 0.01 μmto about 0.03 μm to complete the diffusion barrier. The adhesionpromoter was cured at 165° C. for 2 hours under nitrogen gas flow butwas not annealed so that the polymer surface remained activated for thereaction with copper. Onto the siloxane adhesion promoter, copper metalthin films were deposited to a thickness of 0.3 μm using sputtering ore-beam evaporation. The samples were then subjected to Bias TemperatureStressing (BTS) conditions of 0.5 MV/cm and 150° C. for 1 hr.

EXAMPLE 4

The procedure of Example 3 was followed except that after deposition ofthe copper layer onto the adhesion promoter, the whole structure wasthermally annealed under nitrogen at 250° C. for 1 hr. The samples werethen subjected to Bias Temperature Stressing (BTS) conditions of 0.5MV/cm and 150° C. for 1 hr.

The Triangular Voltage Sweep (TVS) data were recorded for the samples ofExamples 3 and 4 (including an adhesion promoter) and are presented inFIG. 4, which is a graph of capacitance vs. voltage (C vs. V). The datafor the annealed structures of Example 4 are represented as dashedlines, and the data for the structures of Example 3 (no final anneal)are represented by a solid line. Cu diffusion into the siloxane epoxypolymer dielectric was not observed in either case, as indicated by theabsence of a peak in the TVS curve at the BTS. Thus, good adhesion andmetal diffusion barrier properties were achieved.

FIG. 5 is a graph of current density vs. time (I vs. t) for the annealedsamples of Example 4 having an adhesion promoter included in thestructures. As indicated in the graph, the current densities for thesamples are lower than 1×10⁻⁹ Å/cm² at 1 MV/cm and 150° C. for at leastup to 7 hrs. Again this shows that the leakage current property does notdegrade with time. Thus, the samples with adhesion promoter provideadhesion and resist Cu charge injection.

The embodiment described in Example 4 is clearly advantageous becausethe siloxane epoxy polymer (adhesion promoter), when dried, cured, andannealed with the adjacent surface of the copper metal, promotesinteraction with the metal to assure the adhesion. Furthermore, theelectromigration of the metal is surprisingly reduced or eliminatedaltogether. Another advantage afforded by this embodiment is that thediffusion barrier property that prevents the penetration of metal intothe layer of the siloxane epoxy polymer adjacent the adhesion promoteris completely assured.

Each of the patents and patent applications mentioned herein is herebyincorporated by reference in its entirety.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood by thoseskilled in the art that variations and modifications can be effectedwithin the spirit and scope of the invention.

1. A structure comprising a. a conductive layer comprising a conductivemetal; b. a diffusion barrier disposed onto a surface of said conductivelayer, wherein said diffusion barrier comprises a first layer and asecond layer, wherein said first layer is adjacent to said second layerand to said surface of said conductive layer, and wherein said firstlayer and said second layer are each independently selected from thegroup of siloxane epoxy polymers.
 2. The structure of claim 1, whereinsaid first layer is an adhesion promoter having a thickness ranging fromabout 0.001 μm to about 3 μm.
 3. The structure of claim 1, wherein saidfirst layer is an adhesion promoter having a thickness ranging fromabout 0.01 μm to about 0.03 μm.
 4. The structure of claim 1, whereinsaid second layer has a thickness ranging from about 0.02 μm to about 10μm.
 5. The structure of claim 1, wherein said second layer has athickness ranging from about 0.02 μm to about 0.05 μm.
 6. The structureof claim 1, wherein said conductive metal is selected from the groupconsisting of aluminum, aluminum alloys, tungsten, cobalt, metalsilicides, copper, and copper alloys.
 7. The structure of claim 6,wherein said conductive metal is copper or a copper alloy.
 8. Thestructure of claim 1, wherein said group of siloxane epoxy polymersconsists of polymers having formulae (I) and (II)

wherein m is an integer from 5 to 50;

wherein X and Y are monomer units randomly distributed or occurringtogether, R¹ and R² are each independently selected from the group ofmethyl, methoxy, ethyl, ethoxy, propyl, butyl, pentyl, octyl, andphenyl; R³ is methyl or ethyl; p is an integer ranging from 2 to 50; andq is 0 or an integer ranging from 1 to
 50. 9. The structure of claim 8,wherein said first layer of said diffusion barrier is a siloxane epoxypolymer having formula (II), wherein R³ is methyl.
 10. The structure ofclaim 9, wherein R¹ and R² are both methyl groups in formula (II), andthe ratio of p to q ranges from about 8:1 to about 1:1.
 11. Thestructure of claim 10, wherein the ratio of p to q ranges from about 4:1to about 2:1.
 12. The structure of claim 8, wherein said second layer ofsaid diffusion barrier is a siloxane epoxy polymer having formula (II),wherein R³ is methyl.
 13. The structure of claim 12, wherein R¹ and R²are both methyl groups in formula (II), and the ratio of p to q rangesfrom about 8:1 to about 1:1.
 14. The structure of claim 13, wherein theratio of p to q ranges from 4:1 to about 2:1.
 15. The structure of claim8, wherein said first layer of said diffusion barrier is a siloxaneepoxy polymer having formula (I).
 16. The structure of claim 8, whereinsaid second layer of said diffusion barrier is a siloxane epoxy polymerhaving formula (I).
 17. The structure of claim 8, wherein a cationicpolymerization initiator independently selected from the groupconsisting of diazonium, sulfonium, phosphonium, and iodonium salts ispresent with each said siloxane epoxy polymer of said first layer andsaid second layer of said diffusion barrier.
 18. The structure of claim17, wherein each said cationic polymerization initiator is an iodoniumsalt independently selected from the group consisting of diaryliodoniumsalts having formulae (III), (IV), (V), (VI), and (VII)

wherein each R¹¹ is independently hydrogen, C₁ to C₂₀ alkyl, C₁ to C₂₀alkoxyl, C₁ to C₂₀ hydroxyalkoxyl, halogen, and nitro; R¹² is C₁ to C₃₀alkyl or C₁ to C₃₀ cycloalkyl; y and z are each independently integershaving a value of at least 5; and [A]⁻ is a non-nucleophilic anionselected from the group consisting of [BF₄]⁻, [PF₆]⁻, [AsF₆]⁻, [SbF₆]⁻,[B(C₆F₅)₄]⁻, and [Ga(C₆F₅)₄]⁻.
 19. The structure of claim 18, whereineach said selected cationic polymerization initiator is present in acatalyst solution comprising from about 20 to about 60 parts by weightof each said selected cationic polymerization initiator and from about40 to about 80 parts by weight of3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexane carboxylate,dicyclopentadiene dioxide, or bis(3,4-epoxycyclohexyl) adipate.
 20. Thestructure of claim 1, further comprising a dielectric material disposedon an exposed surface of said diffusion barrier.
 21. The structure ofclaim 20, wherein said dielectric material is selected from the groupconsisting of polyimides, parylene (poly-p-xylylene), polynaphthalene,benzocyclobutane (BCB), silicon-containing organic polymers, aromatichydrocarbon polymers, and siloxane epoxy polymers.